Urethane-based adhesive composition

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-110595, filed Jul. 2, 2021, the entire contents of which is incorporated herein by reference.

The present technology relates to a urethane-based adhesive composition.

Conventionally, as an adhesive that can be used for automobiles, an adhesive composition containing a urethane prepolymer, a carbon black, and the like have been known (for example, International Patent Publication No. WO2016/159237).

An adhesive composition for automobiles is usually required to have excellent thermal stability during production, workability and stability during use, physical properties (initial and after-aging) of a cured product to be obtained, and the like, and in recent years, the requirement levels thereof have been increasingly high.

The present inventor has prepared urethane-based adhesive compositions containing a urethane prepolymer, a carbon black, and the like with reference to International Patent Publication No. WO2016/159237, and evaluated the prepared urethane-based adhesive compositions. As a result, it has been found that there is room for improvement of the urethane-based adhesive composition for satisfying all of the above required levels.

The present technology provides a urethane-based adhesive composition having excellent thermal stability during production, workability during use, stability, physical properties (initial and after aging; the same applies hereinafter) of a cured product to be obtained, and adhesiveness.

The present inventor has found that desired effects can be achieved when a urethane-based adhesive composition contains: a urethane prepolymer; carbon blacks A and B each having a dibutyl phthalate oil absorption number in a specific range; a calcium carbonate C; a plasticizer D; a modified product E of aliphatic diisocyanate; and a catalyst, wherein respective contents of A to E are specified, and the contents of A and B satisfy a specific relationship.

The present technology is based on the above finding and the like, and specifically provides the following constitution.

[1] A urethane-based adhesive composition comprising:

[2] The urethane-based adhesive composition according to [1], wherein the modified product E contains a biuret of hexamethylene diisocyanate and/or an isocyanurate of hexamethylene diisocyanate.

[3] The urethane-based adhesive composition according to [1], wherein the calcium carbonate C contains heavy calcium carbonate.

[4] The urethane-based adhesive composition according to [1], wherein the plasticizer D contains a phthalic acid ester and/or an adipic acid ester.

The urethane-based adhesive composition of the present technology is excellent in thermal stability during production, workability during use, stability, physical properties of a cured product to be obtained, and adhesiveness.

The present technology is described in detail below.

In the present specification, a numerical range represented by “(numerical value) to (numerical value)” means a range including the numerical values described before and after “to”.

In the present specification, unless otherwise specified, substances corresponding to each component can be used singly or in combination of two or more kinds thereof. When a component includes two or more substances, the content of the component means the total content of the two or more substances unless otherwise specified.

In the present specification, when at least one of thermal stability during production, workability during use, stability during use, physical properties of a cured product to be obtained, and adhesiveness is more excellent, it may be said that the effect of the present technology is more excellent.

[Urethane-Based Adhesive Composition]

The urethane-based adhesive composition of the present technology (adhesive composition of the present technology) contains: a urethane prepolymer; a carbon black A having a dibutyl phthalate oil absorption number of 30 to 40 ml/100 g; a carbon black B having a dibutyl phthalate oil absorption number of 98 to 108 ml/100 g; a calcium carbonate C; a plasticizer D; a modified product E of an aliphatic diisocyanate; and a catalyst,

In the above (1) to (6), “a” represents the content of the carbon black A, “b” represents the content of the carbon black B, “c” represents the content of the calcium carbonate C, “d” represents the content of the plasticizer D, and “e” represents the content of the modified product E. The “a” is an amount (unit is part by mass) with respect to 100 parts by mass of the urethane prepolymer. The same applies to “b”, “c”, “d”, and “e”.

Hereinafter, each component contained in the adhesive composition of the present technology is described in detail.

[Urethane Prepolymer]

The urethane prepolymer contained in the adhesive composition of the present technology is not particularly limited as long as it is a urethane prepolymer having an isocyanate group. In one of preferred embodiments, the urethane prepolymer has an isocyanate group at a terminal thereof.

Meanwhile, in the present technology, the urethane prepolymer does not contain a modified product E described later.

Examples of the urethane prepolymer include those obtained by having a polyisocyanate reacted with a compound having two or more active hydrogen-containing groups in one molecule (active hydrogen compound) such that the polyisocyanate has an excessive amount of isocyanate group with respect to the active hydrogen-containing group of the active hydrogen compound.

Isocyanate Group Content

The isocyanate group content of the urethane prepolymer is preferably 0.5 to 5 mass % based on the total amount of the urethane prepolymer.

Polyisocyanate

The polyisocyanate used in the production of the urethane prepolymer is not particularly limited as long as it has two or more isocyanate groups in a molecule.

Examples of the polyisocyanate that can be used in the production of the urethane prepolymer include:

Among them, polyisocyanate preferably contains an aromatic polyisocyanate, and more preferably contains MDI, from the viewpoint of excellent curability.

Active Hydrogen Compound

The compound having two or more active hydrogen-containing groups in one molecule (active hydrogen compound) that can be used in the production of the urethane prepolymer is not particularly limited. Examples of the active hydrogen-containing group include a hydroxy (OH) group, an amino group, and an imino group.

Preferable examples of the active hydrogen compound include a polyol compound having two or more hydroxy (OH) groups in one molecule, and among them, a polyol compound is preferable.

The polyol compound that can be used in the production of the urethane prepolymer is not particularly limited as long as it is a compound having two or more hydroxy groups. Examples of the compound include: polyether polyols; polyester polyols; polymer polyols having a carbon-carbon bond in the main chain skeleton, such as acrylic polyols, polybutadiene diols, and hydrogenated polybutadiene polyols; low molecular weight polyhydric alcohols; and mixed polyols of these. Among them, a polyether polyol is one of preferred embodiments.

Examples of the polyether polyol include polyoxyethylene diol (polyethylene glycol), polyoxypropylene diol (polypropylene glycol: PPG), polyoxypropylene triol, an ethylene oxide/propylene oxide copolymer, polytetramethylene ether glycol (PTMEG), polytetraethylene glycol, and sorbitol-based polyol.

Preferred polyether polyols are polypropylene glycol, and polyoxypropylene triol, from the viewpoint of excellent compatibility with polyisocyanate.

The polyether polyol preferably has a weight average molecular weight of 500 to 20,000, from the viewpoint that the viscosity of the urethane prepolymer obtained by the reaction with isocyanate can have moderate fluidity at normal temperature (23° C.). In the present technology, the weight average molecular weight is a polystyrene equivalent value obtained by GPC (Gel Permeation Chromatography) (solvent: tetrahydrofuran (THF)).

The urethane prepolymer preferably contains a urethane prepolymer obtained by reacting a polyether polyol with an aromatic polyisocyanate from the viewpoint of excellent adhesiveness and excellent curability, and more preferably contains a urethane prepolymer obtained by reacting at least one selected from the group consisting of polyoxypropylene diol and polyoxypropylene triol with diphenylmethane diisocyanate.

The method for producing the urethane prepolymer is not particularly limited. For example, a urethane prepolymer can be produced by using polyisocyanate such that 1.5 to 2.5 mol of isocyanate groups react with 1 mol of active hydrogen-containing groups (for example, hydroxy groups) of the active hydrogen compound, and mixing and reacting these.

In producing the urethane prepolymer, a plasticizer D described below may be used.

[Carbon Black A]

In the present technology, the carbon black A is a carbon black having a dibutyl phthalate oil absorption number (DBP oil absorption number) of 30 to 40 ml/100 g.

By containing the carbon black A, the adhesive composition of the present technology is excellent in thermal stability during production, physical properties (for example, shear strength retention) of a cured product to be obtained, and adhesiveness.

Method for Measuring Dibutyl Phthalate Oil Absorption Number of Carbon Black

In the present technology, the dibutyl phthalate oil absorption number of a carbon black was measured in accordance with JIS (Japanese Industrial Standard) K 6217-4: 2008 “Carbon black for rubber industry-Fundamental characteristics-Part 4: Determination of oil absorption number (OAN) and oil absorption number of compressed sample (COAN)”.

Preferred Examples of Carbon Black A

Examples of the carbon black A include carbon blacks of FT and MT grades having a DBP oil absorption number of 30 to 40 ml/100 g.

[Carbon Black B]

In the present technology, the carbon black B is a carbon black having a dibutyl phthalate oil absorption number (DBP oil absorption number) of 98 to 108 ml/100 g.